Dual column gas chromatograph and method for analysis



Dec. 3, 1963 c. T. MAXWELL 3,112,639

DUAL COLUMN GAS CHROMATOGRAPH AND METHOD FOR ANALYSIS Filed Jan. 4, 1960 SAMPLE VENT SQMPL E CREE/P 665 IN /N vs/vro e. CHGRL s5 7710MHS MAXWELL BY HIS HTTOQNEYS. HARRIS, K/ECH, Russ-ELL 6; KEEN United States Patent 3,112,539 DUAL CDLUMN GAS CHRQMATUGRAPH AND METHOD FQR ANALYSiS (Iharles Thomas Maxwell, Anaheim, Calif., assignor to Beckman Instruments, inc, a corporation of California Filed Jan. 4, 1969, Ser. No. 1% 4 Claims. (6i. 73--23) This invention relates to gas chromatography and, in particular, to new and improved dual column gas chromatographs and processes for analyzing samples therewith.

Instruments with two or more columns are being used in gas chromatography to improve the performance where a single column will not provide the desired resolution. In such instruments, the columns will usually have different characteristics, i.e., one column will pass the lower boiling point constituents substantially unresolved but will provide the desired analysis on the higher boiling point constituents, while the second column will resolve the lower boiling point constituents adequately but would require an inordinate amount of time to pass the higher boiling point constituents. In another application of dual column chromatography, one column may be used to resolve the sample into two groups, only one of which is of interest. The group of interest will then be passed through the second column for further analysis while the other group is discarded. In samples Where one or more constituents are present in relatively large quantities, these constituents tend to mask the presence of other constituents present in relatively small quantities and dual column chromatography can be used to separate the higher and lower percentage constituents and provide sensitive analysis of the constituents present in small quantities.

It is an object of the invention to provide new and improved dual column chrornatographs and processes for sample analysis utilizing dual column chromatography. A further object is to provide such apparatus and processes without requiring additional carrier gas lines or iiow restrictors and without requiring substitution of or switching of such lines and restrictors. Another object is to provide such apparatus requiring only the two chromatographic columns, a detector and a valve unit for achieving the various operating modes in dual chromatography. A still further object is to provide analysis processes wherein the desired results are achieved by rearranging of the flow path through the same components.

It is an object or" the invention to provide apparatus and processes wherein a column may be flushed after analysis or sample separation has taken place therein while analysis is continued in a second column. A further object is to provide a dual column chromatograph requiring only a six port valve unit in combination with the two chromatographic columns and a detector. A further object is to provide a dual column chromatograph providing resolution for both high percentage components and low percentage components utilizing a low sensitivity detector and a high sensitivity detector and means for switching the flow path from one detector to the other.

It is an object of the invention to provide a dual column chromatograph and a process for analysis therewith wherein high resolution may be achieved with low resolution columns by recirculating the sample through the first and second columns one or more times to produce the required resolution prior to passing the sample through the detector.

Other objects and novel combinations and arrangements of parts and modes of operation will more fully appear in the course of the following description. The drawing merely shows and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.

In the drawing:

FIG. 1 is a diagrammatic representation of a preferred form of dual column gas chroma-tograph;

FIG. '2 shows the instrument of FIG. I switched to an alternative mode or" operation;

FIGS. 3, 4 and 5 show alternative embodiments of the instrument of FIG. 1;

FIGS. 6 and 7 show two modes of operation of another embodiment of the invention;

FIGS. 8 and 9 show two modes of operation of another embodiment of the invention; and

P16. 10 is a sectional view of one type of valve suitable for use with the invention.

The instrument of FIGS. 1 and 2 includes a first chromatographic column A, a second chromatographic column E, a detector D, a sample introduction valve and another valve in. The valves 15 and 16 may be the same and typically may be a six port valve such as is shown in section in FIG. 10. This valve includes a body 17 and a core 18, with ports Ell-26 in the body and communicating with the core. Three passages 27, 28, 29 are provided in the core 18, with the core being movable from a first position, as shown in EEG. 10, to a second position wherein the ports 21, 26 are connected, the ports 23 2.23 are connected and the ports 25, 24 are connected. in each of FIGS. 1 through 9, the six port valve is shown diagrammatically with the small circles representing the ports and the straight lines between adjacent ports representing the passages in the core. In describing the various embodiments, the ports will be referred to by number but some of the reference numerals will be omitted from the drawing for purposes of clarity.

Referring again to the instrument of FIG. 1, the incoming sample line 32 is connected to the port 21 of the valve l5 and the sample vent line 33 is connected to the port 22. A sample loop in the form of a length of corn duit 34 is connected across the ports 26, 23. The incoming carrier gas line 35 is connected to the port and a gas inlet line 36 is connected between the port 24 of the valve 15' and the port 21 of the valve 16. The column A is connected between the ports 26 and 23 of the valve 16 and the column B is connected in series with the sample chamber of the detector D between the ports 22 and 25. The port 24- is connected through a vent line 37 to exhaust. The incoming carrier gas is also directly connected to the reference chamber of the detector through a line 38. It should be noted that while the embodiment disclosed herein utilizes a dual chamber detector, the invention is equally applicable with any type of gas chromatograph detector.

With the instrument in the configuration of FIG. 1, the sample is passing through the line 34 and pure carrier gas is passing through the columns A and B. When the valve 15' is moved to the other position, as shown in FIG. 2, the sample loop 34 is connected between the lines 35, 36 and the sample contained therein is swept into the gas inlet line 36 by the carrier gas. The valve 16 is maintained in the position of FIG. 1 establishing a flow path from the sample inlet 36 through the column A, the column B, the detector and the vent line 37. Then at a certain time during the analysis cycle, the valve 16 is actuated from the position of FIG. 1 to the position of FIG. 2 to establish a fiow path from the gas inlet 36 through the column B, the detector, the column A and the vent line 37.

The instrument of FIGS. 1 and 2 may be used in conjunction with a sample having some constituents of interest with lower boiling points and some constituents not or" interest with higher boiling points. The column A will be designed to separate the lower boiling point constituents from the higher boiling point constituents, with the lower boiling point constituents passing through the column at a faster rate so as to leave column A and enter column B while the higher boiling point constituents are still in column A. At this time, the valve is actuated to the other position so that the lower boiling point constituents will be resolved in column B and then passed through the detector to provide a record of the individual constituents. At the same time, the higher boiling constituents in column A will be flushed therefrom by the gas leaving the detector so that the instrument will be ready for analyzing another sample in a much shorter time than if all of the constituents, both of higher and lower boiling points, had to pass through column B. A typical example of such an analysis would be a sample containing lower boiling point constituents such as methane, ethane, and ethylene, and higher boiling point constituents such as hexane, propane, and butane, with column A containing carbo wax on firebrick and column B containing alumina.

The low boiling point components passing through the first column, or column A, are extremely volatile and take no longer in passing through column A in the reverse direction than they did passing partially through column A in the forward direction. That is, after the low boiling components have discharged from the second column, or column B, and are again directed into column A, they pass through this column as rapidly as they first passed therethrough before entering column B. The components are completely flushed out of column A almost as quickly as the high boiling components are flushed out of column A. This is true even though column A is backflushed and the high boiling point components have only progressed a short distance through the first column before the direction of flow is reversed and the backflushing operation begins. In this manner it is possible to obtain high resolution of the low boiling point components in the second column while simultaneously carrying out the flushing operation in the first column.

The instrument of FIGS. 1 and 2 provides continuous analysis in column B while eliminating the constituents not of interest and also eliminating the time consumed if such constituents were to pass through the entire instrument. This continuous analysis is achieved without requiring separate carrier gas lines for switching into and out of service and without producing pressure changes in the instrument which would afiect the operation of the columns and the detector.

In the arrangement of FIGS. 1 and 2, gas passes through column A in the same direction in both portions of the operating cycle, producing straight flushing of column A during the second portion of the cycle. FIG. 3 shows an alternative form of the invention wherein column A is backflushed during the second portion of the analysis cycle with the gas passing through column A in a direction opposite to that in the first portion of the cycle. The apparatus is the same as that of FIGS. 1 and 2 except that column B and the detector are connected in series between ports 22 and 24 and the vent line is connected to port 25. FIG. 3 corresponds to FIG. 1 showing the first portion of the analysis cycle with the flow path from the gas inlet 36 through the column A, the column B, the detector and the vent line. When the valve is moved to the other position, the flow path is then through the gas inlet, the column B, the detector, the column A and the vent line, with the direction of flow through column A reversed. This arrangement will be used in analyses where extremely high boiling point constituents are present which constituents are more rapidly flushed rom the column by baclrflushing rather than straight flushing. As in the embodiments of FIGS. 1 and 2, the higher boiling point constituents are continuously analyzed in column B without pressure change problems while column A is flushed.

FIG. 4 shows another form of the dual column chromatograph of the invention suitable for use with samples wherein the higher boiling point constituents are of interest. Column A is connected between the gas inlet line 36 and the port 21, column B is connected between ports 22. and 25, and the detector is connected between ports 25 and 23, with the vent line 37 connected to the port 24. The column A is designed so that the lower boiling point constituents pass therethrough relatively rapidly while the higher boiling point constituents of interest are suitably resolved therein. The valve 16 is initially in the position shown in FIG. 4 so that the lower boiling point constituents pass from column A to column B. When the constituents are thus disposed, the valve is moved to the other position establishing a flow path from the gas inlet through column A, the detector and column B to the vent line so that analysis continues in column A while column B is flushed.

The arrangement of FIG. 4 is also suitable for use wherein it is desired to obtain analysis of both the lower and higher boiling point constituents. For this mode of operation, the valve is maintained in the position of FIG. 4 until all the lower boiling point constituents of interest have been eluted from column B and have passed through the detector. Then the valve is moved to the other position so that the constituents resolved in column A are passed directly to the detector for detection and recording.

The arrangement of FIG. 4 provides for straight flushing of column B during the second portion of the analysis cycle. In FIG. 5, the detector is connected between ports as and 24 and the vent line is connected to port 23, which arrangement provides for backfiushing of column B during the second portion of the analysis cycle. Otherwise, the operation of the embodiments of FIGS. 4 and 5 is the same.

In some samples, some constituents will be present in relatively large quantities while other constituents are present in relatively small quantities. When all of the constituents are analyzed for and recorded in a single instrument, the higher percentage constituents tend to mask the presence of the lower percentage constituents due to tailing eiiects and the like. The arrangements of FIGS. 4 and 5 provide a simple and easy means for eliminating this masking effect. Referring to FIG. 4 the dual column instrument can be operated with the valve in the position of FIG. 4 until the higher percentage constituents not of interest pass into column B. Then before these constituents leave column B and pass to the detector, the valve is moved to the other position so that the higher percentage constituents are flushed to the vent line without ever passing through the detector. Then there will be no tailing efiects and the detector can be operated at a higher sensitivity range to adequately detect and record the lower percentage constituents which are resolved in column A. The same type of analysis may be carried out with the instrument of FIG. 5.

It is sometimes desirable to make analysis for and recordings of both the higher percentage constituents and the lower percentage constituents in a sample. Another form of the invention using a low sensitivity detector D for the higher percentage constituents and a high sensitivity detector D for the lower percentage constituents is shown in FIGS. 6 and 7. The column A is connected between the gas inlet 36 and the port 21 of the valve 16 and the column B is connected between port 22 and the inlet port of a conventional three port valve 42. A low sensitivity detector D is connected between one outlet port of the valve 42 and the vent line 37 and the other outlet port is connected to port of the valve 16 through a line 43. A high sensitivity detector D is connected between ports 26 and 23 and the port 24 is also connected to the vent line 37.

With the valves 16, 42 in the positions of FIG. 6, the lower boiling point constituents are separated from the higher boiling point constituents in column A, and are further resolved in column B and detected for recording in detector D Then the valves are switched to the positions of FIG. 7 so that the higher boiling point constituents are detected for recording in the detector D and the column B is flushed with the eflluent from the detector.

The same arrangement can be used Where the lower boiling point constituents are present in the smaller quantities and the higher boiling point constituents are present in the larger quantities by making the detector D the higher sensitivity detector and the detector D the low sensitivity detector.

FIGS. 8 and 9 show an alternative form of the arrangement of FIGS. 1 and 2, wherein the column B is directly connected between ports 22 and 25 and the sample side of the detector is connected between port 24 and the vent line 37. This form of the invention is particularly suitable for use wherein high resolution is desired with a relatively small physical package. The columns A and B may each be relatively short, and hence of relatively low resolution. The instrument is operated in the condition of FIG. 8 until all of the sample has eluted from column A into column B. Then before the sample begins to leave column B, the instrument is switched to the arrangement of FIG. 9 so that the elutant from column B passes again through column A. When all of the sample is again in column A, the instrument is switched back to the condition of FIG. 8 so that the elutant from column A passes into column B. This switching back and forth may be carried out as many times as necessary to obtain the desired resolution, after which the sample is permitted to pass through the detector 37. While there is no theoretical limit on the number of recirculation cycles that can take place, practical limitations based on the time required for a sample to pass through a column and the time between signal peaks in the elutant will ordinarily limit the recirculation to one to four times. This type of analysis is best suited for samples in which the elution times of the various constituents are relatively close together and the two columns would be identical. The use of two short columns in the manner described above will provide the same resolution as a single column several times the combined size of the two columns. A typical example for this type of analysis would be in the separation of ethane and ethylene. Ordinarily, a single column six feet long and onequarter inch diameter, packed with silica gel, could be used. Usin the present invention, two columns, each six inches in length and one-quarter inch diameter, packed with the same material and operated under the same conditions, will provide the same separations with six cycles of recirculation. The invention is of even greater value when used in place of columns in the forty and fifty foot category where space and temperature control problems are greatly amplified.

Although exemplary embodiments of the invention have been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiments disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

I claim as my invention:

1. A process for analyzing the lower boiling point constituents of a sample having constituents with higher boiling points and constituents with lower boiling points, using gas chromatograph technique with first and second chromatographic columns in conjunction with a single gas inlet, a detector and a single vent line, the process including the steps of: directing the how of carrier and sample gas from the inlet, through the first column, the second column and the detector to the vent line; and when the lower boiling point constituents are in said second column, then directing the flow from the inlet, through said second column, the detector and said first column to the vent line, with the flow through said first column being in a direction opposite to that of the prior step, to continue analysis in said second column while backflushing the higher boiling point constituents from said first column with the elutant flowing from said second column.

2. In a dual column gas chromatograph having a gas inlet, a vent line, and means for introducing a sample into the carrier gas ahead of said gas inlet, the combination of: first and second chromatographic columns; a detector; a six port valve unit movable between first and second positions, with port one connected to port two, port three to port four and port five to port six in said first position, and with port one connected to port six, port three to port two and port five to port four in said second position; conduit means connecting said first column between the gas inlet and port one; conduit means connecting said second column between ports two and five; conduit means connecting said detector between port six and three; and conduit means connecting port four to the vent line whereby the carrier gas is directed serially through said first column, said second column and said detector when said valve unit is in said first position and is directed serially through said second column, said detector and said first column when said valve unit is in said second position.

3. In a gas chromatograph having a gas inlet, a vent line, and means for introducing a sample into the canier gas ahead of said gas inlet, the combination of: first and second chromatographic columns; a detector; a six port valve unit movable between first and second positions and providing three separate flow paths when in said first position and three different flow paths when in said second position; conduit means connecting said detector between said valve unit and the vent line; conduit means connecting the gas inlet to the valve unit; conduit means connecting said first column across a pair of ports of said valve unit; and conduit means connecting said second column across another pair of ports of said valve unit, with said conduit means and said valve unit providing gas flow from the gas inlet, through said first column, said second column and said detector to the vent line when said valve unit is in said second position, and flow from the gas inlet, through said second column, said first column and said detector to the vent line when said valve unit is in said first position, so that a sample may be recirculated through said first and second columns prior to passing through said detector by actuating said valve unit from said second to said first position when the sample is in said second column and actuating said valve unit from said first position to said second position when the sample is again in said first column.

4. In a gas chromatograph having a gas inlet, a vent line, and means for introducing a sample into the carrier gas ahead of said gas inlet, the combination of: first and second chromatographic columns; first and second detectors; a six port valve unit movable between first and second positions and providing three separate flow paths when in said first position and three different flow paths when in said second position; a three port valve unit movable between first and second positions and providing a first fiow path when in said first position and a second flow path when in said second position; and conduit means for connecting said columns, said detectors and said valve units between the gas inlet and the vent line for gas flow through said first column, said second column and said first detector when said valve units are in said first position and through said first column,

s 2,833,151 Harvey May 6, 1958 said second detector and said second column when said 2,981,092 Marks Apr. 25, 1961 OTHER REFERENCES valve units are in said second position, so that the lower boiling point constituents of the sample pass through said first detector and the higher boiling point constituents pass h h i Second detector. 5 Analytical Chemlstry, article by D. H. Lichtenfels et al., Gas Partition Analysis of Light Ends of Gasoline, vol. 28, No. 9, September 1956, pp. 13761379. H Gas Chromatography, book by D. H. Desty, published UNITED SLATES PATENTS in London by Butterworths Scientific Publications, 1958, coggeshau P 27, 1950 US. edition by Academic Press, Inc., New York, pp. Watson et a1 Aug. 7, 1956 10 297 and 293 rah ed References Cited in the file of this patent 

1. A PROCESS FOR ANALYZING THE LOWER BOILING POINT CONSTITUENTS OF A SAMPLE HAVING CONSTITUENTS WITH HIGHER BOILING POINTS AND CONSTITUENTS WITH LOWER BOILING POINTS, USING GAS CHROMATOGRAPH TECHNIQUE WITH FIRST AND SECOND CHROMATOGRAPHIC COLUMNS IN CONJUNCTION WITH A SINGLE GAS INLET, A DETECTOR AND A SINGLE VENT LINE, THE PROCESS INCLUDING THE STEPS OF; DIRECTING THE FLOW OF CARRIER AND SAMPLE GAS FROM THE INLET, THROUGH THE FIRST COLUMN, THE SECOND COLUMN AND THE DETECTOR TO THE VENT LINE; AND WHEN THE LOWER BOILING POINT CONSTITUENTS ARE IN SAID SECOND COLUMN, THEN DIRECTING THE FLOW FROM THE INLET, THROUGH SAID SECOND COLUMN, THE DETECTOR AND SAID FIRST COLUMN TO THE VENT LINE, WITH THE FLOW THROUGH SAID FIRST COLUMN BEING IN A DIRECTION OPPOSITE TO THAT OF THE PRIOR STEP, TO CONTINUE ANALYSIS IN SAID SECOND COLUMN WHILE BACKFLUSHING THE HIGHER BOILING POINT CONSITUENTS FROM SAID FIRST COLUMN WITH THE ELUTANT FLOWING FROM SAID SECOND COLUMN. 